# 6.E: Exercises

- Page ID
- 357323

#### 6.2: Molecular Mass and Formula Mass

- What is the total mass (amu) of carbon in each of the following molecules?
- CH
_{4} - CHCl
_{3} - C
_{12}H_{10}O_{6} - CH
_{3}CH_{2}CH_{2}CH_{2}CH_{3}

- CH

**Answer**-
- 12.01 amu
- 12.01 amu
- 144.1 amu
- 60.05 amu

- What is the total mass of hydrogen in each of the molecules?
- CH
_{4} - CHCl
_{3} - C
_{12}H_{10}O_{6} - CH
_{3}CH_{2}CH_{2}CH_{2}CH_{3}

- CH

**Answer**-
- 4.032 amu
- 1.008 amu
- 10.08 amu
- 12.10 amu

- Calculate the molecular or formula mass of each of the following:
- P
_{4} - H
_{2}O - Ca(NO
_{3})_{2} - CH
_{3}CO_{2}H (acetic acid) - C
_{12}H_{22}O_{11}(sucrose, cane sugar)

- P

**Answer**-
- 123.9 amu
- 18.02 amu
- 164.10 amu
- 60.05 amu
- 342.3 amu

- Determine the molecular mass of the following compounds:

**Answer**-
- 98.91 amu
- 26.04 amu
- 185.8 amu
- 98.09 amu

- Determine the molecular mass of the following compounds:

**Answer**-
- 56.10 amu
- 54.09 amu
- 200.0 amu
- 97.99 amu

- Which molecule has a molecular mass of 28.05 amu?

**Answer**-
molecule b

#### 6.3: Counting Objects By Weighing

- Compare 1 mole of H
_{2}, 1 mole of O_{2}, and 1 mole of F_{2}.- Which has the largest number of molecules? Explain why.
- Which has the greatest mass? Explain why.

**Answer**-
- They all have the same number of molecules. One mole is 6.022 × 10
^{23}particles, regardless of the identity of the particle. - The F
_{2}will have the greatest mass because a molecule of F_{2}weighs more than a molecule of O_{2}or H_{2}.

- They all have the same number of molecules. One mole is 6.022 × 10

#### 6.4: Molar Mass

- How are the molecular mass and the molar mass of a compound similar and how are they different?

**Answer**-
The two masses have the same numerical value, but the units are different: the molecular mass is the mass of 1 molecule in amu while the molar mass is the mass of 6.022 × 10

^{23}molecules in grams.

- Determine the molar mass of each substance.
- Si
- SiH
_{4} - K
_{2}O

**Answer**-
- 28.09 g
- 32.12 g
- 94.20 g

- Determine the molar mass of each substance.
- Cl
_{2} - SeCl
_{2} - Ca(C
_{2}H_{3}O_{2})_{2}

- Cl

**Answer**-
- 70.90 g
- 149.86 g
- 158.17 g

- Determine the molar mass of each substance.
- Al
- Al
_{2}O_{3} - CoCl
_{3}

**Answer**-
- 26.98 g
- 101.96 g
- 165.3 g

- Calculate the molar mass of each of the following compounds:
- hydrofluoric acid, HF
- ammonia, NH
_{3} - nitric acid, HNO
_{3} - silver sulfate, Ag
_{2}SO_{4} - boric acid, B(OH)
_{3}

**Answer**-
- 20.01 g
- 17.03 g
- 63.02 g
- 311.81 g
- 61.83 g

- Calculate the molar mass of each of the following minerals:
- limestone, CaCO
_{3} - halite, NaCl
- beryl, Be
_{3}Al_{2}Si_{6}O_{18} - malachite, Cu
_{2}(OH)_{2}CO_{3} - turquoise, CuAl
_{6}(PO_{4})_{4}(OH)_{8}(H_{2}O)_{4}

- limestone, CaCO

**Answer**-
- 100.09 g
- 58.44 g
- 537.5 g
- 813.4 g

- Calculate the molar mass of each of the following:
- the anesthetic halothane, C
_{2}HBrClF_{3} - the herbicide paraquat, C
_{12}H_{14}N_{2}Cl_{2} - caffeine, C
_{8}H_{10}N_{4}O_{2} - urea, CO(NH
_{2})_{2} - a typical soap, C
_{17}H_{35}CO_{2}Na

- the anesthetic halothane, C

**Answer**-
- 197.38 g
- 257.2 g
- 194.20 g
- 60.06 g
- 306.5 g

#### 6.5: Mole Calculations

- What is the mass of 4.44 mol of Mn?

**Answer**-
244 g

- What is the mass of 0.311 mol of Xe?

**Answer**-
40.8 g

- What is the mass of 12.34 mol of Al
_{2}(SO_{4})_{3}?

**Answer**-
4,222 g

- What is the mass of 0.0656 mol of PbCl
_{2}?

**Answer**-
18.2 g

- How many moles are present in 45.6 g of CO?

**Answer**-
1.63 mol

- How many moles are present in 0.00339 g of LiF?

**Answer**-
1.31 × 10

^{−4}mol

- How many moles are present in 1.223 g of SF
_{6}?

**Answer**-
8.37 × 10

^{−3}mol

- How many moles are present in 48.8 g of BaCO
_{3}?

**Answer**-
0.247 mol

- Determine the mass of each of the following:
- 2.345 g LiCl
- 0.0872 mol acetylene, C
_{2}H_{2} - 3.3 × 10
^{−2}mol Na_{2}CO_{3} - 1.23 × 10
^{3}mol fructose, C_{6}H_{12}O_{6} - 0.5758 mol FeSO
_{4}(H_{2}O)_{7}

**Answer**-
- 99.40 mol
- 2.27 g
- 3.5 g
- 2.22 × 10
^{5}g - 160.1 g

- The approximate minimum daily dietary requirement of the amino acid leucine, C
_{6}H_{13}NO_{2}, is 1.1 g. What is this requirement in moles?

**Answer**-
8.4 × 10

^{−3}mol

- Determine the mass in grams of each of the following:
- 0.600 mol of oxygen atoms
- 0.600 mol of oxygen molecules, O
_{2} - 0.600 mol of ozone molecules, O
_{3}

**Answer**-
- 9.60 g
- 19.2 g
- 28.8 g

- How many moles are present in 54.8 mL of mercury if the density of mercury is 13.6 g/mL?

**Answer**-
3.72 mol

- How many moles are present in 56.83 mL of O
_{2}if the density of O_{2}is 0.00133 g/mL?

**Answer**-
2.36 × 10

^{−3}mol

#### 6.6: Counting Particles By Weighing

- How many atoms are present in 4.55 mol of Fe?

**Answer**-
2.740 × 10

^{24}atoms

- How many atoms are present in 0.0665 mol of K?

**Answer**-
4.00 × 10

^{22}atoms

- How many molecules are present in 2.509 mol of H
_{2}S?

**Answer**-
1.511 × 10

^{24}molecules

- How many molecules are present in 0.336 mol of acetylene (C
_{2}H_{2})?

**Answer**-
2.02 × 10

^{23}molecules

- How many moles are present in 3.55 × 10
^{24}Pb atoms?

**Answer**-
5.90 mol

- How many moles are present in 2.09 × 10
^{22}Ti atoms?

**Answer**-
0.0347 mol

- How many moles are present in 1.00 × 10
^{23}PF_{3}molecules?

**Answer**-
0.166 mol

- How many moles are present in 5.52 × 10
^{25}penicillin molecules?

**Answer**-
91.7 mol

- How many moles are present in 6.411 kg of CO
_{2}? How many molecules is this?

**Answer**-
145.7 mol; 8.772 × 10

^{25}molecules

- How many moles are present in 2.998 mg of SCl
_{4}? How many molecules is this?

**Answer**-
1.724 × 10

^{−5}mol; 1.038 × 19^{19}molecules

- What is the mass in milligrams of 7.22 × 10
^{20}molecules of CO_{2}?

**Answer**-
52.8 mg

- What is the mass in kilograms of 3.408 × 10
^{25}molecules of SiS_{2}?

**Answer**-
5.220 kg

- What is the mass in grams of 1 molecule of H
_{2}O?

**Answer**-
2.992 × 10

^{−23}g

- What is the mass in grams of 1 atom of Al?

**Answer**-
4.480 × 10

^{−23}g

- What is the volume in mL of 3.44 mol of Ga if the density of Ga is 6.08 g/mL?

**Answer**-
39.4 mL

- What is the volume in L of 0.662 mol of He if the density of He is 0.1785 g/L?

**Answer**-
14.8 L

- A 55-kg woman has 7.5 × 10
^{−3}mol of hemoglobin (molar mass = 64,456 g/mol) in her blood. How many hemoglobin molecules is this? What is this quantity in grams?

**Answer**-
4.5 × 10

^{21}molecules; 4.8 × 10^{2}g

- Diamond is one form of elemental carbon. An engagement ring contains a diamond weighing 1.25 carats (1 carat = 200 mg). How many atoms are present in the diamond?

**Answer**-
1.25 × 10

^{22}atoms

- The Cullinan diamond was the largest natural diamond ever found (January 25, 1905). It weighed 3104 carats (1 carat = 200 mg). How many carbon atoms were present in the stone?

**Answer**-
3.113 × 10

^{25}atoms

- One 55-gram serving of a particular cereal supplies 270 mg of sodium, 11% of the recommended daily allowance. How many moles and atoms of sodium are in the recommended daily allowance?

**Answer**-
0.012 mol; 7.1 × 10

^{21}atoms

- A certain nut crunch cereal contains 11.0 grams of sugar (sucrose, C
_{12}H_{22}O_{11}) per serving size of 60.0 grams. How many servings of this cereal must be eaten to consume 0.0278 moles of sugar?

**Answer**-
0.865 servings

- Which of the following represents the least number of molecules?
- 20.0 g of H
_{2}O (18.02 g/mol) - 77.0 g of CH
_{4}(16.06 g/mol) - 68.0 g of CaH
_{2}(42.09 g/mol) - 100.0 g of N
_{2}O (44.02 g/mol) - 84.0 g of HF (20.01 g/mol)

- 20.0 g of H

**Answer**-
20.0 g H

_{2}O

#### 6.7: Using Chemical Formulas as Conversion Factors

- Which contains the greatest mass of oxygen: 0.75 mol of ethanol (C
_{2}H_{5}OH), 0.60 mol of formic acid (HCO_{2}H), or 1.0 mol of water (H_{2}O)? Explain why.

**Answer**-
Formic acid. Its formula has twice as many oxygen atoms as the other two compounds (one each). Therefore, 0.60 mol of formic acid would be equivalent to 1.20 mol of a compound containing a single oxygen atom.

- Which contains the greatest number of moles of oxygen atoms: 1 mol of methanol (CH
_{3}OH), 1 mol of acetic acid (CH_{3}CO_{2}H), or 1 mol of glycerol (C_{3}H_{8}O_{3})? Explain why.

**Answer**-
Glycerol. Each molecule of glycerol has three atoms of oxygen as compared to one atom of oxygen in a molecule of methanol and two atoms of oxygen in acetic acid.

- Determine the number of moles of the compound and determine the number of moles of each type of atom in each of the following:
- 2.12 g of potassium bromide, KBr
- 0.1488 g of phosphoric acid, H
_{3}PO_{4} - 23 kg of calcium carbonate, CaCO
_{3} - 78.452 g of aluminum sulfate, Al
_{2}(SO_{4})_{3} - 0.1250 mg of caffeine, C
_{8}H_{10}N_{4}O_{2}

**Answer**-
- 0.0178 mol KBr; 0.0178 mol K; 0.0178 mol Br
- 1.478 × 10
^{−3}mol H_{3}PO_{4}; 4.433 × 10^{−3}mol H; 1.478 × 10^{−3}mol P; 5.911 × 10^{−3}mol O - 2.3 × 10
^{2}mol CaCO_{3}; 2.3 × 10^{2}mol Ca; 2.3 × 10^{2}mol C; 6.9 × 10^{2}mol O - 0.2293 mol Al
_{2}(SO_{4})_{3}; 0.4586 mol Al; 0.6878 mol S; 2.751 mol O - 6.437 × 10
^{−7}mol caffeine; 5.149 × 10^{−6}mol C; 6.437 × 10^{−6}mol H; 2.575 × 10^{−6}mol N; 1.287 × 10^{−6}mol O

- Determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon, ZrSiO
_{4}, a semiprecious stone.

**Answer**-
zirconium: 2.038 × 10

^{23}atoms; 30.87 g; silicon: 2.038 × 10^{23}atoms; 9.504 g; oxygen: 8.151 × 10^{23}atoms; 21.66 g

- Determine which of the following contains the greatest mass of hydrogen: 1 mol of CH
_{4}, 0.6 mol of C_{6}H_{6}, or 0.4 mol of C_{3}H_{8}.

**Answer**-
1 mol CH

_{4}

- Determine which of the following contains the greatest mass of aluminum: 122 g of AlPO
_{4}, 266 g of Al_{2}Cl_{6}, or 225 g of Al_{2}S_{3}.

**Answer**-
225 g Al

_{2}S_{3}

- A tube of toothpaste contains 0.76 g of sodium monofluorophosphate (Na
_{2}PO_{3}F) in 100 mL.- What mass of fluorine atoms in mg was present?
- How many fluorine atoms were present?

**Answer**-
- 1.0 × 10
^{2}mg F - 3.2 × 10
^{21}atoms F

- 1.0 × 10

#### 6.8: Percent-By-Mass Composition

- A 125 g sample of a compound known to contain only phosphorus and oxygen was shown to contain 54.5 g of phosphorus. What is the percent by mass composition of the compound?

**Answer**-
43.6% P; 56.4% O

- A compound containing only carbon and hydrogen was submitted for analysis. A 1.237 g sample of the compound was found to contain 1.140 g of carbon. What is the percent composition of the compound?

**Answer**-
92.16% C; 7.84% H

- Dichloroethane, a compound that is often used for dry cleaning, contains carbon, hydrogen, and chlorine. A 14.83 g sample of dichloroethane contained 3.60 g of carbon and 0.61 g of hydrogen. What is the percent by mass composition of dichloroethane?

**Answer**-
24.3% C; 4.1% H; 71.6% Cl

- A major textile dye manufacturer developed a new yellow dye containing carbon, nitrogen, and hydrogen. When 16.94 g of the dye was analyzed, it was found to contain 3.00 g of nitrogen and 1.07 g of hydrogen. What is the percent composition of the dye?

**Answer**-
75.98% C; 17.7% N; 6.32% H

#### 6.9: Mass Percent Composition from a Chemical Formula

- Calculate the following to four significant figures:
- the percent composition of ammonia, NH
_{3} - the percent composition of photographic “hypo,” Na
_{2}S_{2}O_{3} - the percent of calcium ion in Ca
_{3}(PO_{4})_{2}

- the percent composition of ammonia, NH

**Answer**-
- 82.25% N; 17.75% H
- 29.08% Na; 40.56% S; 30.36% O
- 38.76% Ca
^{2}^{+}

- Determine the following to four significant figures:
- the percent composition of hydrazoic acid, HN
_{3} - the percent composition of TNT, C
_{6}H_{2}(CH_{3})(NO_{2})_{3} - the percent of SO
_{4}^{2}^{–}in Al_{2}(SO_{4})_{3}

- the percent composition of hydrazoic acid, HN

**Answer**-
- 2.342% H; 97.66% N
- 37.01% C; 2.219% H; 18.50% N; 42.26% O
- 84.23% SO
_{4}^{2−}

- Determine the percent ammonia, NH
_{3}, in Co(NH_{3})_{6}Cl_{3}, to three significant figures.

**Answer**-
38.2% NH

_{3}

- Determine the percent water in CuSO
_{4}∙5H_{2}O to three significant figures.

**Answer**-
36.1% H

_{2}O

- Copper(I) iodide (CuI) is often added to table salt as a dietary source of iodine. How many moles of CuI are contained in 1.00 lb (454 g) of table salt containing 0.0100% CuI by mass?

**Answer**-
2.38 × 10

^{−4}mol CuI

- A cough syrup contains 5.0% ethyl alcohol, C
_{2}H_{5}OH, by mass. If the density of the solution is 0.9928 g/mL, how many grams of ethyl alcohol are contained in a 20.0 mL dose?

**Answer**-
0.99 g ethyl alcohol

- D5W is a solution used as an intravenous fluid. It is a 5.0% by mass solution of dextrose, C
_{6}H_{12}O_{6}, in water. If the density of D5W is 1.029 g/mL, calculate the mass of dextrose in a 1.00 L IV fluid bag.

**Answer**-
51 g dextrose

- Find the mass of sulfuric acid in 325 mL of a 40.0% by mass aqueous solution of sulfuric acid, H
_{2}SO_{4}, for which the density is 1.3057 g/mL.

**Answer**-
1.70 × 10

^{2}g H_{2}SO_{4}

**Contributions & Attributions**

Adapted from "Beginning Chemistry (Ball)" by LibreTexts, licensed under CC BY-NC-SA.

Adapted from "Chemistry (OpenStax)" by LibreTexts, licensed under CC By-NC-SA.

- Vicki MacMurdo (Anoka-Ramsey Community College)
- Lance S. Lund (Anoka-Ramsey Community College)